Query Workbench N1QL always hang on in the main admin UI when memcached bucket present

https://forums.couchbase.com/t/query-workbench-always-hang-on-in-the-main-admin-ui-for-cbe-4-6-3/14487

SELECT COUNT FROM default;

cbq works fine.
I found the error as following:

_time=2017-10-20T01:37:54.491+08:00 _level=ERROR _msg=PrimaryScan.newIndexConnection error=System datastore error - cause: This bucket type is not supported memcached
I do have a Memcached type bucket on the node. when I delete the Memcached bucket.the Query Workbench in the main admin UI works fine.